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Wed, 15 Oct 2025 16:07:53 +0000 Message-ID: <8fab615c-1d78-432b-9acc-01cafe393040@intel.com> Date: Thu, 16 Oct 2025 00:07:37 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/19] sched/fair: Add infrastructure for cache-aware load balancing To: Peter Zijlstra , Madadi Vineeth Reddy CC: Tim Chen , Ingo Molnar , "K Prateek Nayak" , "Gautham R . Shenoy" , Vincent Guittot , "Juri Lelli" , Dietmar Eggemann , Steven Rostedt , Ben Segall , "Mel Gorman" , Valentin Schneider , "Hillf Danton" , Shrikanth Hegde , "Jianyong Wu" , Yangyu Chen , Tingyin Duan , Vern Hao , Len Brown , Aubrey Li , Zhao Liu , Chen Yu , Adam Li , Tim Chen , References: <865b852e3fdef6561c9e0a5be9a94aec8a68cdea.1760206683.git.tim.c.chen@linux.intel.com> <22750d4a-fdd6-48ad-a2ca-aa0c12af329c@linux.ibm.com> <20251015115445.GR3289052@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20251015115445.GR3289052@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KU0P306CA0043.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:29::17) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|DS4PPF990BCE628:EE_ X-MS-Office365-Filtering-Correlation-Id: 38edb303-317d-48c4-6c0d-08de0c04feef X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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>>> +#endif >>> + >>> + /* Next honor the task's cache CPU if it is not included. */ >>> + if (cache_cpu != -1 && !cpumask_test_cpu(cache_cpu, cpus)) >>> + cpumask_or(cpus, cpus, >>> + cpumask_of_node(cpu_to_node(cache_cpu))); >>> + >>> + /* >>> + * Lastly make sure that the task's current running node is >>> + * considered. >>> + */ >>> + if (!cpumask_test_cpu(curr_cpu, cpus)) >>> + cpumask_or(cpus, cpus, cpumask_of_node(cpu_to_node(curr_cpu))); >>> +} >>> + >>> +static void __no_profile task_cache_work(struct callback_head *work) >>> +{ >>> + struct task_struct *p = current; >>> + struct mm_struct *mm = p->mm; >>> + unsigned long m_a_occ = 0; >>> + unsigned long curr_m_a_occ = 0; >>> + int cpu, m_a_cpu = -1, cache_cpu, >>> + pref_nid = NUMA_NO_NODE, curr_cpu; >>> + cpumask_var_t cpus; >>> + >>> + WARN_ON_ONCE(work != &p->cache_work); >>> + >>> + work->next = work; >>> + >>> + if (p->flags & PF_EXITING) >>> + return; >>> + >>> + if (!zalloc_cpumask_var(&cpus, GFP_KERNEL)) >>> + return; >>> + >>> + curr_cpu = task_cpu(p); >>> + cache_cpu = mm->mm_sched_cpu; >>> +#ifdef CONFIG_NUMA_BALANCING >>> + if (static_branch_likely(&sched_numa_balancing)) >>> + pref_nid = p->numa_preferred_nid; >>> +#endif >>> + >>> + scoped_guard (cpus_read_lock) { >>> + get_scan_cpumasks(cpus, cache_cpu, >>> + pref_nid, curr_cpu); >>> + >> >> IIUC, `get_scan_cpumasks` ORs together the preferred NUMA node, cache CPU's node, >> and current CPU's node. This could result in scanning multiple nodes, not preferring >> the NUMA preferred node. > > So this used to be online_mask, and is now magically changed to this > more limited mask. > > Could you split this change out and have it have a justification? OK, we will do this and provide an explanation. thanks, Chenyu